Type 1 diabetes (T1D) is a consequence of autoimmune destruction of pancreatic islet ?-cells and the underlying causes for this process are incompletely understood. Our work suggests novel lipid signaling provided by macrophages and CD4+ T-cells impacts T1D incidence. In particular, the relevant lipids appear to be generated by the Ca2+-independent phospholipase A2? (iPLA2?), which is expressed in immune cells. iPLA2? hydrolyzes membrane phospholipids at the sn-2 position to release a lysophospholipid and a fatty acid. When the fatty acid is arachidonic acid, it can be metabolized to generate bioactive oxidized lipids, or eicosanoids, many of which are pro-inflammatory. We find that (a) an iPLA2?-selective inhibitor, when administered to spontaneous diabetes-prone non-obese diabetic (NOD) mice preserves ?-cell mass, reduces T1D incidence and insulitis, (b) iPLA2? activity promotes M1 macrophage pro-inflammatory phenotype and TNF? production from CD4+ T-cells, (c) macrophage production of select pro-inflammatory eicosanoids (PGE2, leukotrienes, 12-HETE, DHETs) is increased in NOD and reduced in macrophages with reduced iPLA2? (NOD.iPLA2?-/+), (d) T1D incidence is reduced in NOD.iPLA2?-/+, (e) adoptive transfer of NOD.iPLA2?-/- macrophages or splenocytes decreases T1D incidence and improves glucose tolerance. We hypothesize that iPLA2?-derived lipids (iDLs) produced by CD4+/CD8+ T-cells and macrophages play critical roles in T1D development and will address this under the following Aims: 1. Determine the contribution of CD4+/CD8+ T-cell-iDLs to T1D. We propose to utilize CD4+ and CD8+ T-cell preparations from WT and iPLA2?-deficient NOD to (a) determine the requirement of T-cell iDLs for diabetes induction, (b) quantitate T-cell lipid production and identify the iDLs, (c) assess the impact of these select iDLs on islet function and survival. 2. Determine the contribution of macrophage-iDLs to T1D. We propose to (a) utilize macrophage preparations from WT and iPLA2?-deficient NOD to determine the temporal requirement of macrophage iDLs on diabetes induction, (b) assess diabetes development in NOD with selective deficiency in macrophage iPLA2?, (c) determine the impact of select macrophage iDLs on islet function and survival. 3. Assess the impact of CD4+/CD8+ T-cell-or macrophage-derived iDLs on islet iPLA2?. Preliminary results suggest that iPLA2? is induced in stressed ?-cells by NF?B, and PGE2 has been reported to induce NF?B. We will test the possibility that macrophage and/or CD4+/CD8+ T-cell iDLs induce ?-cell iPLA2?, which would be expected to participate in maintaining and amplifying immune responses. We will utilize adoptive transfer, systems level lipidomics, conditional knockouts, immunoblotting, message, IF, and select inhibition of lipid-generating enzymes protocols to address these Aims. R21 Goals. Short-term. Identify and evaluate CD4+/CD8+ T-cell and macrophage iDLs critical for T1D development. Overarching. This could lead to strategies to target and prevent generation of those lipids or modify the responsible lipid-generating enzyme in immune cells, in the context of immunotherapy.